package com.wuhan.template.utils;

import java.io.OutputStream;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.io.PushbackInputStream;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.nio.ByteBuffer;

/**
 * 37 * This class defines the decoding half of character encoders. 38 * A
 * character decoder is an algorithim for transforming 8 bit 39 * binary data
 * that has been encoded into text by a character 40 * encoder, back into
 * original binary form. 41 * 42 * The character encoders, in general, have been
 * structured 43 * around a central theme that binary data can be encoded into
 * 44 * text that has the form: 45 * 46 *
 * <p/>
 * <pre>
 *    47    *      [Buffer Prefix]
 *    48    *      [Line Prefix][encoded data atoms][Line Suffix]
 *    49    *      [Buffer Suffix]
 *    50    *
 * </pre>
 * <p/>
 * 51 * 52 * Of course in the simplest encoding schemes, the buffer has no 53 *
 * distinct prefix of suffix, however all have some fixed relationship 54 *
 * between the text in an 'atom' and the binary data itself. 55 * 56 * In the
 * CharacterEncoder and CharacterDecoder classes, one complete 57 * chunk of
 * data is referred to as a <i>buffer</i>. Encoded buffers 58 * are all text,
 * and decoded buffers (sometimes just referred to as 59 * buffers) are binary
 * octets. 60 * 61 * To create a custom decoder, you must, at a minimum, overide
 * three 62 * abstract methods in this class. 63 *
 * <DL>
 * 64 *
 * <DD>bytesPerAtom which tells the decoder how many bytes to 65 * expect from
 * decodeAtom 66 *
 * <DD>decodeAtom which decodes the bytes sent to it as text. 67 *
 * <DD>bytesPerLine which tells the encoder the maximum number of 68 * bytes per
 * line. 69 *
 * </DL>
 * 70 * 71 * In general, the character decoders return error in the form of a 72
 * * CEFormatException. The syntax of the detail string is 73 *
 * <p/>
 * <pre>
 *    74    *      DecoderClassName: Error message.
 *    75    *
 * </pre>
 * <p/>
 * 76 * 77 * Several useful decoders have already been written and are 78 *
 * referenced in the See Also list below. 79 * 80 * @author Chuck McManis 81 * @see
 * CEFormatException 82 * @see CharacterEncoder 83 * @see UCDecoder 84 * @see
 * UUDecoder 85 * @see BASE64Decoder 86
 */

public abstract class CharacterDecoder
{

    /**
	 * Return the number of bytes per atom of decoding
     */
    abstract protected int bytesPerAtom();

    /**
     * Return the maximum number of bytes that can be encoded per line
     */
    abstract protected int bytesPerLine();

    /**
     * decode the beginning of the buffer, by default this is a NOP.
     */
    protected void decodeBufferPrefix(PushbackInputStream aStream,
                                      OutputStream bStream) throws IOException
    {
    }

    /**
     * decode the buffer suffix, again by default it is a NOP.
     */
    protected void decodeBufferSuffix(PushbackInputStream aStream,
                                      OutputStream bStream) throws IOException
    {
    }

    /**
     * 103 * This method should return, if it knows, the number of bytes 104 *
     * that will be decoded. Many formats such as uuencoding provide 105 * this
     * information. By default we return the maximum bytes that 106 * could have
     * been encoded on the line. 107
     */
    protected int decodeLinePrefix(PushbackInputStream aStream,
                                   OutputStream bStream) throws IOException
    {
        return (bytesPerLine());
    }

    /**
     * 113 * This method post processes the line, if there are error detection 114
     * * or correction codes in a line, they are generally processed by 115 * this
     * method. The simplest version of this method looks for the 116 * (newline)
     * character. 117
     */
    protected void decodeLineSuffix(PushbackInputStream aStream,
                                    OutputStream bStream) throws IOException
    {
    }

    /**
     * 121 * This method does an actual decode. It takes the decoded bytes and 122
     * * writes them to the OutputStream. The integer <i>l</i> tells the 123 *
     * method how many bytes are required. This is always <= bytesPerAtom(). 124
     */
    protected void decodeAtom(PushbackInputStream aStream, OutputStream bStream,
                              int l) throws IOException
    {
        throw new IOException();
    }

    /**
     * 130 * This method works around the bizarre semantics of
     * BufferedInputStream's 131 * read method. 132
     */
    protected int readFully(InputStream in, byte buffer[], int offset, int len) throws IOException
    {
        for (int i = 0;
             i < len;
             i++)
        {
            int q = in.read();
			if (q == -1)
			{
				return ((i == 0) ? -1 : i);
			}
            buffer[i + offset] = (byte) q;
        }
        return len;
    }

    /**
     * 145 * Decode the text from the InputStream and write the decoded 146 *
     * octets to the OutputStream. This method runs until the stream 147 * is
     * exhausted. 148 * @exception CEFormatException An error has occured while
     * decoding 149 * @exception CEStreamExhausted The input stream is
     * unexpectedly out of data 150
     */
    public void decodeBuffer(InputStream aStream, OutputStream bStream) throws IOException
    {
        int i;
        int totalBytes = 0;

        PushbackInputStream ps = new PushbackInputStream(aStream);
        decodeBufferPrefix(ps, bStream);
        while (true)
        {
            int length;

            try
            {
                length = decodeLinePrefix(ps, bStream);
                for (i = 0;
                     (i + bytesPerAtom()) < length;
                     i += bytesPerAtom())
                {
                    decodeAtom(ps, bStream, bytesPerAtom());
                    totalBytes += bytesPerAtom();
                }
                if ((i + bytesPerAtom()) == length)
                {
                    decodeAtom(ps, bStream, bytesPerAtom());
                    totalBytes += bytesPerAtom();
                }
                else
                {
                    decodeAtom(ps, bStream, length - i);
                    totalBytes += (length - i);
                }
                decodeLineSuffix(ps, bStream);
            }
            catch (IOException e)
            {
                break;
            }
        }
        decodeBufferSuffix(ps, bStream);
    }

    /**
     * 182 * Alternate decode interface that takes a String containing the encoded
     * 183 * buffer and returns a byte array containing the data. 184 * @exception
     * CEFormatException An error has occured while decoding 185
     */
    public byte decodeBuffer(String inputString)[]throws IOException
    {
        byte inputBuffer[] = new byte[inputString.length()];
        ByteArrayInputStream inStream;
        ByteArrayOutputStream outStream;

        inputString.getBytes(0, inputString.length(), inputBuffer, 0);
        inStream = new ByteArrayInputStream(inputBuffer);
        outStream = new ByteArrayOutputStream();
        decodeBuffer(inStream, outStream);
        return (outStream.toByteArray());
    }

    /**
     * 199 * Decode the contents of the inputstream into a buffer. 200
     */
    public byte decodeBuffer(InputStream in)[]throws IOException
    {
        ByteArrayOutputStream outStream = new ByteArrayOutputStream();
        decodeBuffer(in, outStream);
        return (outStream.toByteArray());
    }

    /**
     * 208 * Decode the contents of the String into a ByteBuffer. 209
     */
    public ByteBuffer decodeBufferToByteBuffer(String inputString) throws IOException
    {
        return ByteBuffer.wrap(decodeBuffer(inputString));
    }

    /**
     * 216 * Decode the contents of the inputStream into a ByteBuffer. 217
     */
    public ByteBuffer decodeBufferToByteBuffer(InputStream in) throws IOException
    {
        return ByteBuffer.wrap(decodeBuffer(in));
    }
}